1. Field of the Invention
This invention relates to apparatus for processing semiconductor wafers, including an improved gas distribution plate used to introduce gas into a semiconductor processing chamber. More particularly, this invention relates to a gas distribution plate used to introduce gas into a semiconductor wafer processing chamber, which serves as an electrode when plasma processing is carried out in the chamber, and which contains means for inhibiting arcing at the gas distribution plate surface and means for inhibiting blockage of process gases passing through the gas distribution plate to the processing chamber.
2. Description of the Related Art
In the processing of semiconductor wafer, for example, to etch the wafer or to deposit a layer on material on the wafer surface, one or more gases are introduced into the processing chamber through openings in a gas distribution plate facing the wafer surface being processed. To assist in such etching or deposition, a plasma is often ignited in the chamber between the gas distribution plate and the wafer, for example, by electrically connecting the gas distribution plate to an RF power source, while grounding the metal walls of the chamber, as well as the wafer support on which the wafer rests during such processing.
The openings in the gas distribution plate, through which the processing gas flows into the chamber, are conventionally arranged in a symmetrical pattern of circular holes which are generally all of the same diameter to ensure even flow and distribution of the gases into the chamber. FIG. 1 shows such a prior art gas distribution plate 2 having a symmetrical arrangement of circular openings 4 formed therein.
While such a symmetrical pattern of identical circular openings generally serves to provide an even distribution of gas flow into the processing chamber, problems have been encountered with such circular openings. It has been found, for example, that the diameter of the circular openings must be maintained within a certain range which is not always convenient for the amount of desired gas flow into the processing chamber. If the diameter of the circular openings is less than about 508 micrometers (.mu.m) or 0.020 inches (20 mils), the formation of by-products, by reaction of the halogen-containing plasmas with the wafer and/or chamber wall, will often result in blockage of at least some of the holes, resulting in either a reduced gas flow, or an unevenly distributed gas flow, or both, which may, in turn, affect process results.
On the other hand, the obvious solution to a blockage problem, i.e., increasing the diameter of the circular holes, can result in arcing on the gas distribution plate caused by the unstable plasma which can either flow along the face of the plate, or go into the gap between the plate and the lid or top of the processing chamber, if the diameter of the circular holes is about 762 .mu.m (30 mils) or larger. This leaves a margin of less than about 254 .mu.m (10 mils) in hole diameter between potential blockage of the openings, if the openings are too small, and potential arcing if the openings are too large.
It would, therefore, be desirable to provide a semiconductor processing apparatus suitable for use with plasma processing wherein the gas distribution plate of the apparatus was provided with a pattern of openings therein of sufficient size and shape to permit the flow of gas therethrough into the chamber, without blockage of the openings, regardless of the type of plasma generated in the chamber, while still inhibiting arcing of the plasma on the surface of the gas distribution plate and with a larger dimensional margin of opening sizes.